+### C5 Cellular Configuration
+
+The ModemConfigurationCommand message allows users to change certain aspects of modem operation on-the-fly (at runtime). The modem configuration settings are stored in flash memory and are untouched by the bootloader during a software update (assuming the correct cellular_c5 linker file is used during compilation of vi-firmware). Thus, new modem settings persistent across power cycles.
+
+The ModemConfigurationCommand message provides three sub-messages for particular groups of modem settings. These are NetworkOperatorSettings, NetworkDataSettings, and ServerConnectSettings. These configuration messages are described in great detail within the [c5_cellular_config](https://github.com/openxc/vi-firmware/docs/advanced/c5_cell_config.html) documentation.
+
+Currently, only the ServerConnectSettings sub-message is supported in the vi-firmware's command interpreter. All other settings are currently compile-time only.
+
+The ServerConnectSettings part of ModemConfigurationCommand allows the user to set the host server name and port that the device will use when opening a TCP socket to upload data. This destination must be running an HTTP server similar to [OpenXCWebServer](https://github.com/openxc/openxc-azure-webserver), which defines a set of supported HTTP transactions where the body is comprised of data in the familiar OpenXC Message Format.
+
+**Request**
+
+ { "command": "modem_configuration",
+ "server": {
+ "host": "www.myhost.com",
+ "port": 10000
+ }
+ }
+
+**Response**
+
+ { "command_response": "modem_configuration", "status": true}
+
+## C5 SD Card Status
+
+In order to check the status of the SD card, the following command is available:
+
+ { "command": "sd_mount_status"}
+
+Command response if the SD card is mounted correctly:
+
+ { "command_response": "sd_mount_status", "status": true}
+
+If the SD card is full, not enabled, or connected as a MSD, the device will respond with:
+
+ { "command_response": "sd_mount_status", "status": false}
+
+For more info see [c5_msd](https://github.com/openxc/vi-firmware/docs/advanced/msd.html).
+
+## C5 RTC Configuration
+
+To set the current time of the RTC, the following
+
+ { "command": "rtc_configuration", "unix_time": "1448551563"}
+
+The response is
+
+ { "command_response": "rtc_configuration", "status": true}
+
+For more info see [c5_rtc](https://github.com/openxc/vi-firmware/docs/advanced/rtc.html).
+
+## Extra Values
+
+Any of the following JSON objects may optionally include an `extras`
+field. The value may be any valid JSON object or array. The client libraries
+will do their best to parse this information into a generic format and pass it
+to your application. For example:
+
+ {"name": "steering_wheel_angle",
+ "value": 45,
+ "extras": {
+ "calibrated": false
+ }
+ }
+